| 48001. |
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| 48002. |
- Hursin, Mathieu, et al.
(författare)
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Measurement of the gas velocity in a water-air mixture in crocus by neutron noise technique
- 2019
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M and C 2019. ; , s. 2696-2703
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Konferensbidrag (refereegranskat)abstract
- © 2019 American Nuclear Society. All rights reserved. The possibility to measure the gas phase velocity in a two-component mixture with neutron noise techniques is demonstrated in the zero-power reactor CROCUS of the Ecole Polytechnique Federale de Lausanne. It is the first step toward the experimental validation of a theoretical method aiming at the reconstruction of the void profile in a BWR channel. For this experiment, a channel is installed in the water reflector of CROCUS and two-component mixtures are generated inside the channel through injection of air at various flow rates. The signal fluctuations of two neutron detectors located at different elevations next to the channel are recorded and their Cross Power Spectral Density analyzed with various techniques to determine the transit time of the gas phase and its velocity. Experimental results are compared with predictions obtained with the TRACE thermal-hydraulic code. Results disagree in their magnitudes but the evolution of the gas velocity with the air injection rate are similar.
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| 48003. |
- Hursin, Mathieu, et al.
(författare)
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Measurement of the Gas Velocity in a Water-Air Mixture in CROCUS Using Neutron Noise Techniques
- 2020
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 206:10, s. 1566-1583
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of measuring the gas-phase velocity in a two-phase mixture through the use of neutron noise techniques is demonstrated in the zero-power reactor CROCUS of the Ecole Polytechnique Federale de Lausanne. It is the first step toward the experimental validation of an existing theoretical model whose objective is the reconstruction of the void profile in a channel. The use of zero-power research reactors is advantageous due to their clean environment in terms of signal fluctuations. To this end, a channel was installed in the reflector of CROCUS. A two-component mixture is generated inside the channel through the injection of compressed air. The signal fluctuations of neutron detectors located at various axial locations next to the channel are processed to determine the transit time of the gas phase between detectors. Four methods are presented based on the detector signal time series either in the time domain (time correlations between signals) or in the frequency domain (phase of the cross-power spectral density. All four methods returned consistent transit times and similar experimental uncertainty. The largest possible gas injection rates as well as the highest possible neutron flux level improve the visibility of the traveling perturbation and reduce the experimental uncertainty on the transit time for a given acquisition time. © 2020, © 2020 American Nuclear Society.
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| 48004. |
- Hursin, Mathieu, et al.
(författare)
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Modeling noise experiments performed at AKR-2 and CROCUS zero-power reactors
- 2023
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Ingår i: Annals of Nuclear Energy. - 0306-4549 .- 1873-2100. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- CORTEX is a EU H2020 project (2017-2021) devoted to the analysis of ’reactor neutron noise’ in nuclear reactors, i.e. the small fluctuations occurring around the stationary state due to external or internal disturbances in the core. One important aspect of CORTEX is the development of neutron noise simulation codes capable of modeling the spatial variations of the noise distribution in a reactor. In this paper we illustrate the validation activities concerning the comparison of the simulation results obtained by several noise simulation codes with respect to experimental data produced at the zero-power reactors AKR-2 (operated at TUD, Germany) and CROCUS (operated at EPFL, Switzerland). Both research reactors are modeled in the time and frequency domains, using transport or diffusion theory. Overall, the noise simulators managed to capture the main features of the neutron noise behavior observed in the experimental campaigns carried out in CROCUS and AKR-2, even though computational biases exist close to the region where the noise-inducing mechanical vibration was located (the so-called ”noise source”). In some of the experiments, it was possible to observe the spatial variation of the relative neutron noise, even relatively far from the noise source. This was achieved through reduced uncertainties using long measurements, the installation of numerous, robust and efficient detectors at a variety of positions in the near vicinity or inside the core, as well as new post-processing methods. For the numerical simulation tools, modeling the spatial variations of the neutron noise behavior in zero-power research reactors is an extremely challenging problem, because of the small magnitude of the noise field; and because deviations from a point-kinetics behavior are most visible in portions of the core that are especially difficult to be precisely represented by simulation codes, such as experimental channels. Nonetheless the limitations of the simulation tools reported in the paper were not an issue for the CORTEX project, as most of the computational biases are found close to the noise source.
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| 48005. |
- Hursin, Mathieu, et al.
(författare)
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Validation of axial void profile measured by neutron noise techniques in crocus
- 2020
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Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 1586-1593
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Konferensbidrag (refereegranskat)abstract
- Recently a joint project has been carried out between the Paul Scherrer Institut, the Ecole Polytechnique Federale de Lausanne and swissnuclear, an industrial partner, in order to determine the axial void distribution in a channel installed in the reflector of the zero power research reactor CROCUS, using neutron noise techniques. The main objective of the present paper is to report on the validation of the results against an alternative measurement technique using gamma-ray attenuation and simulations with the TRACE code. For the gamma-ray attenuation experiments, the channel used in CROCUS is installed out of the core in a Plexiglass water tank. The source and detector are fixed and the channel is moved axially to keep the geometry of the source/detector arrangement untouched. This is key to measure the void effect by gamma attenuation due to the low contrast of this technique. The paper compares the experimental results obtained with both techniques, with the outcomes of simulations carried out with the TRACE code. Even though the quantitative void fraction estimations are not consistent, the trends obtained with the simulation and experimental techniques are the same. The discrepancies between the various experimental techniques and the simulation outcomes are related to the heterogeneous distribution of the water-air mixture in the radial sections of the channel.
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| 48006. |
- Hurtig, Eva, 1949
(författare)
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Hemhörighet och stadsförnyelse: belyst i fyrtiotalsstadsdelen Sanna i Göteborg
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The dissertation explores the concept of home, how relations to one's home are created and what feeling at home means. The thesis' methodology and background to understanding are inspired by phenomenology. The urban renewal of Göteborg's Sanna quarter, built in the 1940's, sets the stage for a description of how a sense of feeling at home emerges in various ways through a feeling of belonging and how these feelings are affected by urban renewal. The information is primarily based on interviews, discussions in different situations with tenants and other involved parties as well as observations made during the lengthy renovation process, 1982-86. Experiences of urban renewal show that tenants homes are not sufficiently safeguarded during reno-vation. The final discussion concerns demands that ought to be made of urban renewal based on the experiences gained. The thesis should function as a source of inspiration and draw atten-tion to the meaning of home to people. My hope is that it will contri-bute to an adaptation of urban renewal in consideration of the signi-ficance of people's homes.
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| 48007. |
- Hurtig, Johan, 1974, et al.
(författare)
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Electrophoretic transport in surfactant nanotube networks wired on microfabricated substrates
- 2006
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 78:15, s. 5281-5288
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Tidskriftsartikel (refereegranskat)abstract
- Nanofluidic devices are rapidly emerging as tools uniquely suited to transport and interrogate single molecules. We present a simple method to rapidly obtain compact surfactant nanotube networks of controlled geometry and length. The nanotubes, 100- 300 nm in diameter, are pulled from lipid vesicles using a micropipet technique, with multilamellar vesicles serving as reservoirs of surfactant material. In a second step, the nanotubes are wired around microfabricated SU-8 pillars. In contrast to unrestrained surfactant networks that minimize their surface free energy by minimizing nanotube path length, the technique presented here can produce nanotube networks of arbitrary geometries. For example, nanotubes can be mounted directly on support pillars, and long stretches of nanotubes can be arranged in zigzag patterns with turn angles of 180 degrees. The system is demonstrated to support electrophoretic transport of colloidal particles contained in the nanotubes down to the limit of single particles. We show that electrophoretic migration velocity is linearly dependent on the applied field strength and that a local narrowing of the nanotube diameter results from adhesion and bending around SU-8 pillars. The method presented here can aid in the fabrication of fully integrated and multiplexed nanofluidic devices that can operate with single molecules.
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| 48008. |
- Hurtig, Johan, 1974, et al.
(författare)
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Injection and Transport of Bacteria in Nanotube-Vesicle Network
- 2008
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 4:7, s. 1515-1520
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Tidskriftsartikel (refereegranskat)abstract
- Microinjection of bacteria (the MG1655 strain of E. coli.) into unilamellar lipid vesicles contained in surface-immobilized nanotube-vesicle networks is demonstrated. Injected baceria can not escape from one vesicle to another as the size of interconnecting nanotubes is too small (~200 nm in diameter) to allow for entry. Bacteria can, however, be moved from one vesicle to another by using Marangoni flows. Thus, single or several species can be transferred to a neighboring vesicle at will. The technique offers new possibilities for live matter functionalization into synthetic host networks, and may provide a means of studying the effect of compartmentalization and chemical species on a single bacterium. Thus, it may serve as an experimental platform to study how vesicle-encapsulated bacteria evade destruction in macrophages or how bacteria surf along thin membrane nanotubes toward connected macrophage cell bodies
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| 48009. |
- Hurtig, Johan, 1974
(författare)
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Nanotube Vesicle Networks: Immobilization and Transport Studies
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surfactant lipids are an essential element of living cells. They are the basis for the biomembranes that envelope and divide cells into compartments. In addition to this static function, lipid membranes also play a role in dynamic processes such as transport and signaling. The development of biomimetic lipid nanotube vesicle networks and the techniques involved has been an ongoing process for over 10 years. The techniques have expanded and our abilities to observe, handle, and predict nanotube vesicle network processes have increased. The applications of these systems range from the basic research of biological membrane behavior and cellular processes to the development of pharmaceutical drugs in a user friendly medical industry environment.This thesis explores and expands techniques and applications of lipid nanotube vesicle mainly with a focus on immobilization and transport. Networks of nanotubes and vesicles offer a platform for construction of biomimetic nanofluidic devices operating down to single molecule and particle level. Highly organized and well defined lipid vesicle networks can be constructed with control over connectivity, container size, content, tube lengths and angle between nanotubes. Transport of fluid and particles confined in the network nodes can be controlled with several methods as well as modifications of content by controlled injections or chemical reaction dynamics.Among these are the pipette writing principle described in paper I, allowing fast and efficient formation and immobilization of well defined networks with regard to size, geometry and connectivity. The method developed in paper II aid in the fabrication of fully integrated and multiplexed nanofluidic devices and expands the vesicle network connectivity to the third dimension. In paper III the use of electrophoretic transport show linear velocities of transported latex beads. Moreover it is proven that nanotubes adhered to a specific epoxy surface does not collapse and can sustain transport. Nanotubes wired to microfabricated substrates are shown to introduce new functionalities to vesicle networks. Based on the experimental observations and theoretical modeling in paper IV, we conclude that Y junctions observed in nanotube-vesicle networks forms by a zipper-like mechanism. Surfactants from two branches flow through the junction and form the extension of the third nanotube branch. The incorporation of an entirely biological component into the nanotube vesicle network in paper V not only shows proof of concept but also introduces new functionality to the system. The motile bacteria E. coli can be electroinjected into unilamellar lipid vesicles retaining both viability and motility. It is also suggested that they can be utilized to alter the chemical environment.
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| 48010. |
- Hurtig, Johan, 1974
(författare)
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Patterning and Controlled Adhesion of Cells and Lipid Nanotube Vesicle Networks by Microfabricated Substrates
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Networks of nanotubes and vesicles offer a platform for construction of nanofluidic devicesoperating on single molecule and particle level. Here one has the opportunity to study chemistryin confined biomimetic compartments in an environment as close to nature as possible withoutgoing in-vivo.The development of lipid vesicle networks and the techniques involved has been an ongoingprocess for over 10 years. Over the years weve expanded our abilities to observe, handle, andpredict nanotube vesicle networks. Understanding of the physical properties of these systems isimperative to the explanation of the observed behavior in the conducted experiments. But werequickly approaching the limit where we also require knowledge of how these systems act andreact to their environment. If we want to use these systems for anything more than just as cooltoy we need to get a grip on the hard physical aspects of how we choose to interact with thesesystems.The research in highly organized lipid vesicle networks is going into a regime where control ofsurface properties becomes a fundamental interest. Without proper attention to the substrate wewill never achieve our scientific goals, the use of these systems in a user friendly, research ormedical industry environment, where they can be used in the research of biological membranebehavior and cellular processes for the development of medical drugs.The scientific field of lipid nanotube vesicle networks has taken several major steps toward atechnique that is of use for the general scientific community. Among these are the cell patterningcovered in paper I, concerning electroporation of cells, the pipette writing principle described inpaper II, and in paper III, the expansion of vesicle networks to the third dimension.
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